U.S. patent application number 11/137236 was filed with the patent office on 2005-12-01 for hub unit for use in electrically movable wheels and vehicle comprising the hub unit.
This patent application is currently assigned to Sanyo Electric Co., Ltd.. Invention is credited to Adachi, Ryohei, Tanaka, Tatsuaki, Tomoshige, Kazuhiro.
Application Number | 20050264111 11/137236 |
Document ID | / |
Family ID | 34936930 |
Filed Date | 2005-12-01 |
United States Patent
Application |
20050264111 |
Kind Code |
A1 |
Tanaka, Tatsuaki ; et
al. |
December 1, 2005 |
Hub unit for use in electrically movable wheels and vehicle
comprising the hub unit
Abstract
A hub unit for use in electrically assisted bicycles has an
improved effect to radiate heat from a stator. A hub (7) has inner
teeth (66a) meshable with planetary gears (65) and a fixing support
shaft (57) projecting from opposite ends of the hub and provided
fixedly relative to a motor housing (5). The motor housing (5) has
no cylindrical wall (8) covering the outer peripheral surface of
the stator (3) but leaves the stator outer peripheral surface
exposed to effectively release the heat generated by the windings
of the stator.
Inventors: |
Tanaka, Tatsuaki;
(Kasai-shi, JP) ; Tomoshige, Kazuhiro; (Kasai-shi,
JP) ; Adachi, Ryohei; (Kanzaki-Gun, JP) |
Correspondence
Address: |
ECKERT SEAMANS CHERIN & MELLOTT
600 GRANT STREET
44TH FLOOR
PITTSBURGH
PA
15219
|
Assignee: |
Sanyo Electric Co., Ltd.
Osaka
JP
|
Family ID: |
34936930 |
Appl. No.: |
11/137236 |
Filed: |
May 25, 2005 |
Current U.S.
Class: |
310/75C ;
310/216.004; 310/216.114; 310/216.127; 310/216.133; 310/67A;
310/83 |
Current CPC
Class: |
Y02T 10/64 20130101;
H02K 7/1846 20130101; H02K 5/04 20130101; Y02T 10/705 20130101;
B62M 6/65 20130101; Y02T 10/7005 20130101; B60L 3/0061 20130101;
B60L 50/20 20190201; H02K 9/00 20130101; B60L 2200/12 20130101;
Y02T 10/70 20130101; B62J 6/12 20130101; B60L 50/52 20190201; H02K
9/14 20130101; B60L 2240/36 20130101; H02K 7/116 20130101; B60L
50/66 20190201; Y02T 10/641 20130101 |
Class at
Publication: |
310/075.00C ;
310/067.00A; 310/083; 310/216 |
International
Class: |
H02K 007/00; H02K
007/06 |
Foreign Application Data
Date |
Code |
Application Number |
May 27, 2004 |
JP |
2004-156966 |
Claims
1. An electrically movable wheel hub unit comprising a motor
composed of a stator and a rotor, a hub enclosing the motor therein
and rotatingly drivable by the rotation of the rotor, and a fixing
support shaft disposed on an axis of rotation of the hub and
projecting from the motor housing fixedly relative thereto, the
support shaft projecting outward beyond the hub, the motor housing
comprising a pair of end plates opposed to each other with a stack
of metal plates of the stator held therebetween and fastened to
each other by tightening up bolts to cause the end plates to clamp
the metal plate stack therebetween, the stator having an outer
peripheral surface left exposed to face an inner surface of the hub
between the end plates.
2. The electrically movable wheel hub unit according to claim 1
wherein the metal plate stack comprises units each having a
specified number of metal plates blanked out, and the units are
stacked as displaced from one another in the direction of rotation
by a predetermined angle.
3. The electrically movable wheel hub unit comprising a motor
composed of a stator and a rotor, a hub enclosing the motor therein
and rotatingly drivable by the rotation of the rotor, and a fixing
support shaft disposed on an axis of rotation of the hub and
projecting from the motor housing (5) fixedly relative thereto, the
support shaft projecting outward beyond the hub, the motor housing
comprising a pair of end plates positioned on an axis of the stator
and opposed to each other with the stator held therebetween, and
spacer rods 50 positioned between the end plates and arranged at
equal intervals circumferentially of the stator, the spacer rods
and the end plates being fastened together by tightening up bolts,
the stator having an outer peripheral surface left exposed to face
an inner surface of the hub between the end plates and between each
adjacent pair of spacer rods.
4. The electrically movable wheel hub unit according to claim 3
wherein the metal plate stack is provided in an outer peripheral
surface thereof with grooves for the respective spacer rods to fit
in.
5. The electrically movable wheel hub unit according to claims
.quadrature. wherein the hub has enclosed therein a planetary gear
mechanism operable by the rotation of the rotor, the hub having
inner teeth formed on an inner surface thereof and meshable with
planetary gears of the planetary gear mechanism.
6. A vehicle comprising a wheel having incorporated therein an
electrically movable wheel hub unit according to any one of claim
1.
7. A vehicle comprising a wheel having incorporated therein an
electrically movable wheel hub unit according to any one of claim
2.
8. A vehicle comprising a wheel having incorporated therein an
electrically movable wheel hub unit according to any one of claim
3.
9. A vehicle comprising a wheel having incorporated therein an
electrically movable wheel hub unit according to any one of claim
4.
10. A vehicle comprising a wheel having incorporated therein an
electrically movable wheel hub unit according to any one of claim
5.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to hub units for use in
electrically movable wheels, and to electrically assisted bicycles,
wheelchairs and like vehicles comprising the hub unit.
BACKGROUND OF THE INVENTION
[0002] FIG. 9 shows an electrically movable wheel hub unit 2 for an
electrically assisted bicycle.
[0003] The electrically movable wheel hub unit (hereinafter
referred to as the "hub unit") has a motor 9 comprising a stator 3
and a rotor 4, a hub 7 enclosing the motor 9 therein and rotatingly
drivable at a reduced speed by the motor 9 and a planetary gear
reduction mechanism 6, and fixing support shafts 57, 57a disposed
on the axis of rotation of the hub 7 fixedly relative to a motor
housing 5 and projecting outward from the hub 7.
[0004] The stator 3 comprises a stack 31 of metal plates and
windings 32 provided on the metal plate stack 3.
[0005] The motor housing 5 comprises a cylindrical wall 8 and a
pair of end plates 51, 52 closing opposite end openings of the wall
8. The end plates 51, 52 are fastened to the cylindrical wall 8
with bolts 53b, 53b.
[0006] The metal plate stack 31 of the stator 3 is fastened to one
of the end plates, 51, with a plurality of bolts 53d extending
through the outer peripheral portion of the stack.
[0007] The fixing support shafts 57, 57a extending through
respective opposite ends of the hub 7 are fixed to the front or
rear fork of the bicycle, and the spokes (not shown) of the wheel
are fitted into spoke attaching holes 74a in circumferential walls
74, 74 provided around the outer periphery of the hub 7.
[0008] When windings 32 of the stator 3 are energized, the rotor 4
rotates. The rotation of the rotor 4 is transmitted to the hub 7
upon a speed reduction by the planetary gear reduction mechanism 6
to rotate the wheel of the bicycle.
[0009] In the case where a load not smaller than a specified value
acts on the pedals of the bicycle when they are stepped on, the
windings 32 of the stator 3 are energized, permitting the rider to
run with ease even on slopes.
[0010] See, for example, JP-A No. 2002-514550.
[0011] The energization of the windings results in heat
generation.
[0012] If the windings 32 are overheated, the rotor 4 can not be
rotated with high toque, hence a need for a contrivance for
releasing the heat of the windings 32.
[0013] However, since the stator 3 is enclosed in the motor housing
5 which is closed, the stator 3 is unable to radiate heat
effectively.
[0014] For this reason, it is practice to enclose a cooling liquid
within the hub 7 to cool the motor housing 5 from outside and
suppress the heat generation of the windings 32.
[0015] When the cooling liquid is enclosed in the hub 7, means or
measure is needed for preventing leakage of the liquid to result in
a corresponding increase in cost. The cooling liquid used
correspondingly increases the weight of the hub unit.
[0016] The present invention provides a hub unit of the type
described wherein the outer peripheral surface of the stator 3 is
left exposed to face the inner surface of the hub 7, with the
cylindrical wall 8, part of the motor housing 5, dispensed with so
as to cause the stator 3 to release heat more effectively for the
prevention of overheating. The invention also provides a vehicle
comprising the hub unit.
SUMMARY OF THE INVENTION
[0017] The present invention provides a hub unit 2 comprising a
motor 9 composed of a stator 3 and a rotor 4, a hub 7 enclosing the
motor therein and rotatingly drivable by the rotation of the rotor
4, and a fixing support shaft 57 disposed on an axis of rotation of
the hub 7 and projecting from the motor housing 5 fixedly relative
thereto, the support shaft 57 projecting outward beyond the hub
7.
[0018] The motor housing 5 comprises a pair of end plates 51, 52
opposed to each other, with a stack 31 of metal plates of the
stator 3 held therebetween, and fastened to each other by
tightening up bolts to cause the end plates 51, 52 to clamp the
metal plate stack 31 therebetween.
[0019] The stator 3 has an outer peripheral surface left exposed to
face an inner surface of the hub 7 between the end plates 51,
52.
[0020] The motor housing 5 has no cylindrical wall 8 surrounding
the outer peripheral surface of the metal plate stack 31 of the
stator 3, so that even in the event of the windings of the stator 3
generating heat, the heat can be effectively released through the
stator 3 to the outside of the motor housing 5, consequently
preventing the windings 32 from overheating.
[0021] This obviates the need to suppress the overheating of the
windings 32 by the conventional means, i.e., a cooling liquid
enclosed within the hub 7.
[0022] Because the cylindrical wall 8 of the motor housing 5 can be
dispensed with and further because there is no need for time and
labor for enclosing the cooling liquid in the hub, the hub unit can
be manufactured at a reduced cost. The hub unit can be obtained
also with a weight reduction corresponding to the cylindrical wall
8 and the cooling liquid omitted.
[0023] The stator 3 can be given an increased outside diameter
corresponding to the absence of the cylindrical wall 8, with the
result that increased torque is available.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] FIG. 1 is a front view of an electrically assisted
bicycle;
[0025] FIG. 2 is a sectional view of a hub unit;
[0026] FIG. 3 is a perspective view of the hub unit with a hub main
body removed;
[0027] FIG. 4 is a perspective view of the hub unit;
[0028] FIG. 5 is an exploded perspective view of a stack of metal
plates;
[0029] FIG. 6 is a sectional view of a hub unit of second
embodiment;
[0030] FIG. 7 is a perspective view of the hub unit with a hub main
body removed;
[0031] FIG. 8 is a sectional view of a hub unit of third
embodiment;
[0032] FIG. 9 is a sectional view of a conventional hub unit;
and
[0033] FIG. 10 is a perspective view of the hub unit with a hub
main body removed.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0034] FIG. 1 shows an example of electrically assisted bicycle 1
having a hub unit 2 of the present invention.
[0035] A hub unit 2 is attached to the lower end of a front fork 12
of the bicycle 1, and the hub unit 2 and the rim 13 of a front
wheel 11 are interconnected by spokes 14, 14.
[0036] A battery 17 is mounted on the bicycle between a seat post
15 and a rear wheel 16.
[0037] A sensor (not shown) is provided on a suitable portion on
which the pedaling force of the pedals 18 acts for energizing a
motor 9 of the hub unit 2 by the battery 17 when the load on the
pedals is not smaller than a predetermined value.
[0038] The hub unit 2, which basically has the same construction as
the conventional example of FIG. 9, has the above-mentioned motor 9
which comprises a stator 3 and a rotor 4, a hub 7 enclosing the
motor 9 therein and rotatingly driven by the rotation of the rotor
4, and a fixing support shaft 57 secured to a motor housing 5,
projecting therefrom in alignment with the axis of rotation of the
hub 7 and extending outward from the hub 7.
[0039] The stator 3 has a metal plate stack 31 which comprises a
specified number of metal plates 31a blanked out as shown in FIG. 5
and as already known. Each of the metal plates 31a is in the form
of a ring having a plurality of T-shaped projections 31b arranged
on the inner periphery of the ring at equal intervals
circumferentially thereof and projecting toward the center of the
ring. The metal plate 31a has twelve projections 31b according to
the present embodiment.
[0040] A winding 32 is provided on a stack of projections 31b in
phase as a unit.
[0041] Such a metal plate stack 31 is made conventionally by
blanking out metal plates 31a from a metal sheet material with a
blanking die and stacking the plates as blanked out at the same
time.
[0042] For this reason, burrs created on respective adjacent pairs
of blanked-out metal plates 31a, 31a are located at the same
position or in alignment.
[0043] If burrs are formed on each single blanked-out metal plate
31a uniformly circumferentially thereof, the metal plate stack 31
will have a uniform thickness circumferentially thereof.
[0044] However, this is almost unlikely in actuality; when a single
blanked-out metal plate 31a is observed, burrs are not positioned
uniformly with respect to the circumferential direction. When metal
plates 31a which are blanked out in succession are merely stacked
in superposed layers, the single metal plate stack 31 will have a
difference of about 0.1 to 0.3 mm in thickness and has a portion of
large thickness and a portion of small thickness.
[0045] For the reason to be given later, there is a need to reduce
the likelihood that the metal plate stack 31 will have a portion of
large thickness and a portion of small thickness. Accordingly, the
stack 31 is divided into units 31c each comprising a number of
blanked-out metal plates 31a, and the units 31c are stacked as
displaced from one another through a predetermined angle.
[0046] According to the present embodiment, the units 31c are
stacked as displaced from one another through an angle obtained by
dividing 360 deg by the number of units 31c to make the metal plate
stack 31. For example, in the case where the number of units 31c is
three, the three units 31c are displaced from one another by 120
deg, and a wire is wound around each of the projection stacks 31b
to form the winding 32.
[0047] The metal plate stack 31 can be made easily by blanking out
metal plates 31a from a metal sheet material, stacking a specified
number of blanked-out metal plates 31a upon blanking, rotating the
metal sheet material through a predetermined angle, e.g., through
120 deg according to the present embodiment, within a horizontal
plane every time the specified number of metal plates are blanked
out.
[0048] Incidentally, the number of inward projections 31b on the
metal plate 31b blanked out is limited to a number which can be
divided by the number of units 31c.
[0049] The rotor 4 is rotatably disposed inside the stator 3
concentrically therewith.
[0050] The rotor 4 is made by inserting a rotating shaft 41 through
the center of a stack 42 of circular metal plates so as to render
the shaft 41 rotatable with the metal plate stack 42.
[0051] A plurality of permanent magnets 43 are embedded in the
outer peripheral portion of the metal plate stack 42 in parallel to
the rotating shaft 41 at equal intervals with S poles and N poles
arranged alternately circumferentially of the stack.
[0052] The housing 5 for the motor 9 is made by holding the metal
plate stack 31 of the stator 3 between a pair of first and second
end plates 51, 52 opposed to each other axially of the stator 3 and
fastening the two end plates 51, 52 together with a plurality of
bolts 53 inserted through the outer peripheral portion of the stack
31 and tightened up.
[0053] The metal plate stack 31 of the stator 3 serves the function
of fixedly positioning the first end plate 51 and the second end
plate 52 as spaced apart by a given distance. Thus, the metal plate
stack 31 serves also the function of a cylindrical wall 8 of the
motor housing 5 in the conventional hub unit shown in FIG. 9.
[0054] The first end plate 51 and the second end plate 52 are
provided with respective bearings 58, 58 inside the center portions
thereof for the bearings 58, 58 to support opposite ends of the
rotating shaft 41 of the rotor 4.
[0055] The first end plate 51 and the second end plate 52 are
provided at their outer peripheral edges with short inward cylinder
portions 54, 55, respectively. The short cylinder portions 54, 55
have at their inner ends respective stepped portions 54a, 55a
having fitted therein opposite-end outer peripheral edges of the
metal plate stack 31.
[0056] The first end plate 51 has a boss 56 on the outer side of
the center portion thereof. Extending through the boss 56 is a
fixing support shaft 57 projecting outward. The shaft 57 is
externally threaded as at 57b.
[0057] Provided externally of the second end plate 52 is a
reduction mechanism for transmitting the rotation of the rotor 4 to
the hub 7 upon a speed reduction.
[0058] The reduction mechanism of the present embodiment is a
planetary gear reduction mechanism 6.
[0059] The reduction mechanism 6 has a planetary gear support frame
61 provided with three tubular legs 62 projecting toward and
bearing against the second end plate 52 and equidistantly spaced
circumferentially of the frame. The frame 61 is fastened to the
second end plate 52 with bolts 63 extending through the respective
legs 62.
[0060] Extending between and supported by the second end plate 52
and the planetary gear support frame 61 are three support shafts 64
equidistantly spaced circumferentially of the second end plate 52
and each adapted to rotatably support a planetary gear 65
thereon.
[0061] The planetary gear 65 comprises a large gear 65a positioned
closer to the second end plate 52 and a small gear 65b positioned
on the opposite side and coaxial with the gear 65a.
[0062] The large gear 65a of the planetary gear 65 is in mesh with
a sun gear 60 formed on an end portion of the rotating shaft 41 of
the rotor 4. The small gear 65b of the planetary gear 65 is in mesh
with inner teeth 66a on the closure plate 72 of the hub 7 to be
described later.
[0063] The planetary gear support frame 61 has a boss 67 on the
inner side of the center portion thereof. Extending through the
center of the boss 67 is a fixing support shaft 57a projecting
outward. The shaft 57a is externally threaded as at 57b.
[0064] The hub 7 comprises a hub main body 71 generally in the form
of a cup which is open at the center of its bottom wall and open
over the entire area of the other side, and the above-mentioned
closure plate 72 covering the entire opening.
[0065] The hub main body 71 covers the motor housing 5 and the
planetary gear reduction mechanism 6. A bearing 73 is provided in
the bottom opening 70 around the boss 56 on the first end plate 51
of the motor housing 5.
[0066] The closure plate 72 covers the entire opening of the hub
main body 71 so as to conceal the support frame 61 of the reduction
mechanism 6 and is fastened to the hub main body 71 with bolts
76.
[0067] Fastened with screws to the inner side of the closure plate
72 is an annular member 66 concentric with the fixing support shaft
57. The inner teeth 66a meshable with the planetary gears 65 are
formed on the inner periphery of the annular member 66.
[0068] The fixing support shaft 57a on the support frame 61 extends
through the closure plate 72 to the outside. A bearing 75 is
provided in the closure plate 72 around the fixing support shaft
57a.
[0069] The hub main body 71 has a circumferential wall 74 formed on
its outer peripheral surface and extending therearound at each of
opposite side portions. Spoke attaching holes 74a are formed in the
circumferential wall 74 and arranged at regular intervals
circumferentially of the wall.
[0070] With reference to FIG. 2, the rotating shaft 41 of the rotor
4, the fixing support shaft 57 on the first end plate 51 of the
motor housing 5, and the fixing support shaft 57a extending through
the closure plate 72 of the hub 7 are arranged in alignment.
[0071] When both the fixing support shafts 57, 57a are secured to
the front fork 12 of the bicycle by screw-thread engagement, the
portions marked with lines slanting leftwardly downward in FIG. 2
are fixed portions, and the portions marked with lines slanting
rightwardly downward are rotating portions.
[0072] When a load in excess of a specified value acts on the
bicycle pedals 18 upon the pedals being stepped on, the battery 17
energizes the windings 32 of the stator 3, rotating the rotor
4.
[0073] The rotation of the rotor 4 rotates the sun gear 60 on the
end of the rotating shaft 41 to rotate the planetary gears 65 in
position. The rotation of the planetary gears 65 is transmitted
through the inner teeth 66a to the hub 7 on a speed reduction,
drivingly rotating the front wheel 11.
[0074] By virtue of the rotation of the rotor 4, the bicycle 1 can
be run with a reduced stepping force on the pedals 11.
[0075] The energization of the windings 32 causes the windings 32
to generate heat, which is given to the stator 3. However, the
motor housing 5 does not have a cylindrical wall which prevents
radiation of heat, so that the heat given to the stator 3 is
released directly through an opening between the pair of end plates
51, 52 holding the stator 3 therebetween, whereby the windings 32
can be prevented from overheating without necessitating the cooling
liquid conventionally enclosed in the hub 7.
[0076] Because the cylindrical wall 8 of the motor housing 5 can be
dispensed with and further because there is no need for time and
labor for enclosing the cooling liquid in the hub, the hub unit can
be manufactured at a reduced cost. The hub unit can be obtained
also with a weight reduction corresponding to the cylindrical wall
8 and the cooling liquid omitted.
[0077] The stator 3 can be given an increased outside diameter
corresponding to the absence of the cylindrical wall 8, with the
result that increased torque is available.
[0078] If the metal plate stack 31 of the stator 3 has varying
thicknesses circumferentially thereof, the parallelism between the
end plates 51, 52 involves errors, which produce a bending force
acting on the rotating shaft 41 of the rotor 4 supported by
bearings 58, 58 on the opposed end plates 51, 52, giving rise to
the problem of causing trouble to the smooth rotation of the rotor
4. For this reason, an inherent problem will arise when the metal
plate stack 31 of the stator 3 is held between the pair of end
plates 51, 52 and if the end plates 51, 52 are fastened together by
tightening up the bolts 53 so as to cause the thrust of screws to
act on the stack 31 in the direction of stacking as practiced in
the present embodiment.
[0079] According to the embodiment, however, a plurality of units
31c each comprising a specified number of metal plates 31a blanked
out are stacked as displaced from one another by a predetermined
angle so as to render the metal plate stack 31 uniform in thickness
circumferentially thereof to the greatest possible extent. Even if
the end plates 51, 52 are fastened by tightening up the bolts 53 so
as to causes the thrust of screws to act on the metal plate stack
31 in the stacking direction, the first and second end plates 51,
52 can therefore be given parallelism with high accuracy.
[0080] Consequently, the rotor 4 can be rotated smoothly by giving
improved parallelism to the bearings 58, 58 for supporting the
opposite ends of the rotating shaft 41 of the rotor 4.
[0081] FIG. 6 shows a second embodiment of hub unit 2, and FIG. 7
is a perspective view of the same with a hub main body removed.
[0082] This embodiment has the same construction as the hub unit 2
shown in FIG. 2 except the motor housing 5 and the means for
attaching the metal plate stack 31 of the stator 3 to the motor
housing. Accordingly, the same description will not be given
repeatedly.
[0083] The motor housing 5 comprises a first end plate 51, second
end plate 52, a plurality of spacer rods 50 interposed between the
two end plates 51, 52 for determining the distance therebetween,
and fastening bolts 53b, 53b inserted through the end plate 51 or
52 and screwed into the spacer rods 50.
[0084] The spacer rods 50 have a length slightly larger than the
thickness of the metal plate stack 31 of the stator 3.
[0085] The metal plate stack 31 is provided in its outer peripheral
portion with grooves 33 for the respective spacer rods to fit
in.
[0086] The stack 31 is fastened to the first end plate 51 or the
second end plate 52 with bolts 53a extending through the outer
peripheral portion of the stack 31.
[0087] The metal plate stack 31 does not serve also as a component
of the motor housing 5 unlike the stack 31 of the hub unit 2 shown
in FIG. 2.
[0088] In the case of the embodiment of FIG. 6, therefore, no
bending force will act on the rotating shaft 41 of the rotor 4 even
if the stack 31 has varying thicknesses circumferentially
thereof.
[0089] FIG. 8 shows a third embodiment of hub unit 2. This
embodiment has the same construction as the hub unit 2 shown in
FIG. 2 except that a single fixing support shaft 57 extends through
a hub 7 and that a rotor 4 is provided on a tubular shaft 44
rotatably fitting around the support shaft 57.
[0090] When the fixing support rods 57, 57a extend through
respective opposite ends of the hub 7 to project outward therefrom
and are each independent of the rotating shaft 41 of the rotor 4 as
in the hub unit 2 shown in FIG. 2, the hub unit has a complex
construction. Furthermore, errors involved in machining or
assembling the components are likely to cause the deflection of the
axes of the support shafts 57, 57a at the opposite ends, whereas
the third embodiment can be free of these problems.
[0091] The hub unit 2 of the present invention, which is useful for
electrically assisted bicycles, can be embodied alternatively for
hubs for vehicles having wheels, for example, for wheelchairs.
[0092] The individual fixing support shafts 57, 57a of the first
and second embodiments described are caused to extend outward from
respective opposite ends of the hub 7, and the single fixing
support rod 57 of the third embodiment has opposite ends projecting
from respective opposite ends of the hub 7, so that the hub unit 2
can be supported at opposite ends, whereas when the hub unit 2 is
to be supported at only one end thereof as in wheelchairs, one end
of the fixing support shafts is omitted.
[0093] Apparently, the present invention can be modified and
altered by one skilled in the art without departing from the spirit
of the invention, and such modification is included within the
scope of the invention as set forth in the appended claims.
* * * * *